Various medical procedures involve the infusion of a liquid into the patient and the measurement of blood pressure. For example, in the intravenous administration of a liquid, the desired liquid is transmitted from a bag or other container through flexible tubing and a needle to the vein of a patient. Flow control of the liquid can be obtained by various components, including separate stop cocks and flush valves, and a separate pressure transducer may be employed to measure blood pressure.
The use of separate individual components for controlling liquid flow through the tubing to the patient adds to the complexity of the system. In addition, the separate components make operation of the system more difficult and may tend to increase the likelihood of operator error.
The flow control function may require a capability for restricted or drip flow, flush or high-volume flow, no flow, and venting. Drip flow may be required for, among other things, to prevent occlusion of the needle or other instrument inserted into the patient. High volume or flush flow may be required, for example, to flush bubbles from the system or to clean the tubing and connected components. The vent mode is usable, for example, for calibrating pressure sensing equipment. Although these modes of operation could be provided as four different rotational positions of a rotary valve, the valve may have to be larger than desired in order to provide these four positions with appropriate seals and orifice sizes. Also, a rotary valve of this type may not permit fail safe operation in which the valve cannot unintentionally be left in the flushing position.